Impact of Advanced Impregnation Technologies on the Bioactivity, Bioaccessibility, and Quality of a Hydrolyzed Collagen-Enriched Apple Snack

The increasing demand for functional foods with added health benefits has driven the development of innovative food products. This study aimed to develop a functional snack made from Granny Smith apples enriched with hydrolyzed collagen using impregnation technologies, including vacuum impregnation (VI), ultrasound (US), and moderate electric field (MEF), and pretreatment with CO₂ laser microperforations (MPs) combined with drying methods, including conventional drying (CD) and refractance window drying (RW). The collagen content increased significantly across treatments, with MP-I achieving the highest retention (79.86 g/100 g db). Compared with VI-CD (3.8 mg GAE/g db), MP-RW drying resulted in more total polyphenols (up to 7.2 mg GAE/g db), which was attributed to its shorter drying time (55 min vs. 160 min). The RW treatments also better-preserved color quality, with higher a* (red tones) and b* (yellow tones) values, especially in the MP-RW and US-RW treatments, highlighting their advantages in maintaining visual appeal. Texture analysis revealed that RW drying produced slices with reduced hardness and increased crispness, with MP-RW resulting in the highest sensory crispness score (8.3). In vitro digestion demonstrated that the (VI) treatment resulted in the highest degree of collagen bioaccessibility (~90%), underscoring the effectiveness of this method in improving nutrient delivery compared with the 65% MP, ~70% US, and ~74% methods. The ~90% bioaccessibility is particularly noteworthy, as it indicates that a significant portion of the impregnated collagen remains available for absorption, reinforcing the potential of VI as a strategy for developing functional foods with enhanced nutritional benefits.